1. Field of the Invention
The present invention relates to the field of display technology, and more particular to a thin-film transistor (TFT) substrate and a manufacturing method thereof.
2. The Related Arts
With the progress of the display technology, flat panel display devices, such as liquid crystal displays (LCDs), due to various advantages, such as high image quality, low power consumption, thin device body, and wide range of applications, have been widely used in all sorts of consumer electronic products, including mobile phones, televisions, personal digital assistants (PDAs), digital cameras, notebook computers, and desktop computers, making them the main stream of display devices.
Most of the liquid crystal display devices that are currently available in the market are backlighting LCDs, which comprise a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is that with liquid crystal molecules disposed between two parallel glass substrates and multiple vertical and horizontal tiny conductive wires arranged between the two glass substrates, electricity is applied to control direction change of the liquid crystal molecules for refracting out light emitting from the backlight module to generate an image.
The liquid crystal display panel is made up of a color filter (CF) substrate, a thin-film transistor (TFT) substrate, liquid crystal (LC) interposed between the CF substrate and the TFT substrate, and sealant and is generally manufactured with a process involving an anterior stage of array engineering (for thin film, photolithography, etching, and film peeling), an intermediate stage of cell engineering (for lamination of the TFT substrate and the CF substrate), and a posterior stage of module assembly (for combining a drive integrated circuit (IC) and a printed circuit board). Among these stages, the anterior stage of array engineering generally involves the formation the TFT substrate for controlling the movement of liquid crystal molecules; the intermediate stage of cell engineering generally involves filling liquid crystal between the TFT substrate and the CF substrate; and the posterior stage of module assembly generally involves the combination of the drive IC and the printed circuit board for driving the liquid crystal molecules to rotate for displaying images.
Organic light-emitting diode (OLED) displays, which also referred to organic electroluminescent displays, are a newly emerging flat panel display device and demonstrates prosperous future applications due to advantages including easy manufacturing operation, low cost, low power consumption, high luminous brightness, wide range of adaptation of working temperature, compact size, fast response, each realization of color displaying and large-screen displaying, easy realization of combination with integrated circuit drives, and easy realization of flexible displaying.
An OLED is generally made up of a substrate, an anode arranged on the substrate, a hole injection layer arranged on and anode, a hole transport layer arranged on the hole injection layer, an emissive layer arranged on the hole transport layer, an electron transport layer arranged on the emissive layer, an electron injection layer arranged on the electron transport layer, and a cathode arranged on the electron injection layer. The principle of light emission of an OLED display device is that when a semiconductor material and an organic light emission material are driven by an electric field, carrier currents are injected and re-combine to cause emission of light. Specifically, the OLED display device often uses an indium tin oxide (ITO) pixel electrode and a metal electrode to respectively serve as the anode and cathode of the device and electrons and holes, when driven by a predetermined electrical voltage, are respectively injected into the electron transport layer and the hole transport layer such that the electrons and the holes respectively migrate through the electron transport layer and the hole transport layer to get into the emissive layer and meet in the emissive layer to form excitons that excites light emissive molecules to emit light, the later undergoing radiation relaxation to give off visible light.
Based on the way of driving, OLEDs can be classified in two categories, passive matrix OLED (PMOLED) and active matrix OLED (AMOLED), namely one for direct addressing, and the other for TFT array addressing, among which, the AMOLED comprises pixels that are arranged in an array and belongs to an active display type, having high light emission performance and being commonly used in high definition large-sized display devices.
TFTs are the primary drive elements that are currently used in liquid crystal display devices and active matrix organic light-emitting diode display devices and are directly related to the trend of development of high performance flat panel display devices. Indium gallium zinc oxide (IGZO) has various advantages, including high mobility, applicability to manufacturing in large areas, and easy adaption of amorphous silicon (a-Si) manufacturing processes and is current a hot spot of researches conducted in the field of thin-film transistor technology. However, an IGZO active layer of an IGZO TFT is very sensitive to manufacturing operation and environment and it is often necessary to use an etch stop (ES) layer and involve an additional mask to protect the IGZO active layer, this being adverse to cost reduction of a TFT manufacturing process. Further, due to stacking between source/drain (S/D) terminals and the etch stop (ES) layer, the size of a channel of the TFT device must be made relatively large and parasitic capacitance is also increased. Further, due to the forbidden bandwidth of IGZO (which is around 3.4 eV) being close to the forbidden bandwidth of ultraviolet (UV) light, IGZO shows excellent absorption of UV light and an IGZO active layer, when irradiated with UV light, would cause valence-band electrons to readily jump to conduction band through absorption of energy, resulting in threshold voltage shifting of a TFT and making the display performance of a display unstable.